1. Field of the Invention
The present invention relates to a solid electrolytic capacitor and a method of manufacturing a solid electrolytic capacitor, and particularly to a solid electrolytic capacitor having an ionic liquid and a method of manufacturing a solid electrolytic capacitor having an ionic liquid.
2. Description of the Related Art
A solid electrolytic capacitor has conventionally widely been known as a capacitor suitable for reduction in size. A solid electrolytic capacitor has an anode element having a dielectric film formed on a surface thereof and further has a solid electrolyte between the anode element and a cathode layer.
An anode element obtained by etching a metal plate or a metal foil of a valve metal, an anode element obtained by sintering molded valve metal powders, and the like are available as an anode element, and a dielectric film can be formed by subjecting a surface of such an anode element to electrolytic oxidation. The dielectric film thus formed is extremely dense, high in durability, and very thin. Therefore, as compared with other capacitors such as a paper capacitor and a film capacitor, the solid electrolytic capacitor can be reduced in size without lowering capacitance.
Manganese dioxide, a conductive polymer and the like have been known as a material for a solid electrolyte. In particular, electric conductivity of a solid electrolyte composed of a conductive polymer such as polypyrrole, polyaniline or polythiophene is high and hence an equivalent series resistance (hereinafter referred to as “ESR”) of the solid electrolytic capacitor can be lowered.
A conductive polymer layer can lower ESR of the solid electrolytic capacitor, whereas the conductive polymer layer itself does not have ion conductivity. Therefore, the conductive polymer layer cannot have capability of repairing a damaged dielectric film, that is, an anodic oxidation function. Thus, a solid electrolytic capacitor having a conductive polymer layer is disadvantageously lower in withstand voltage performance than other solid electrolytic capacitors.
A technique making use of an ionic liquid has been expected as a technique for solving the problem above. The ionic liquid is a salt molten and kept in a liquid state in an environment at room temperature and it has such characteristics as non-volatility and high ion conductivity. Therefore, presence of an ionic liquid in a conductive polymer layer can allow a damaged portion of the dielectric film to be repaired and the ionic liquid is considered to be able to enhance withstand voltage performance of a solid electrolytic capacitor. Japanese Patent Laying-Open No. 2008-283136 describes a technique relating to a solid electrolytic capacitor having a conductive polymer layer containing an ionic liquid, as a technique using such an ionic liquid.
A high-performance solid electrolytic capacitor has also currently increasingly been demanded, and further technical development has been demanded.